The subject invention relates generally to valves used in transferring granular and powdered stock and more particularly, but not by way of limitation, to an airlock valve which provides for transferring of the stock between two operations and maintaining a pressure differential therebetween.
Heretofore, two common types of airlock valves have been used in the transferring of granular and powdered stock which maintain a seal between two operations having different pressures. The most common type of airlock valve used in material handling of this type is a rotary vane airlock valve. This type of valve is satisfactory in most cases except for the handling of abrasive materials.
When handling abrasive materials (such as sand, powdered clay, and various types of crushed ore), a flap valve or gate-lock valve is used. These types of valves involve a greater initial expense because of their inherent complexity and greater maintenance cost because of worn and broken replacement parts caused by the jamming of the valve. The flap-type valve requires two trap doors, one below the other. These doors are synchronized to alternately open and close allowing material to drop through from one chamber to the next. The driving mechanism of these type valves is mounted outside the stock chambers and require shafts to pass through the enclosed walls of the chambers with bearings to support the shaft and rotary seals to seal the shafts. The shafts are connected to a drive linkage with counter weights or springs and a driver. This construction with its moving parts is subject to wear, especially the seals and bearings which are in contact with the abrasive dust from the stock. Also, the upper door must try to seal against a continuous flow of material since there is no provision for shutting off the flow into the upper chamber.
Another limitation inherent to the design of the flap-type valves is caused by the large door area compared to the area of flow. This area must be large to allow sufficient material flow. However, this limits the practical pressure differential that the valves can work since the doors have to open against the force created by the pressure multiplied by the area of the opening. To open against high pressure differentials would require extremely heavy drive components. This limitation has been overcome by stage opening or having two doors on one gate. The smaller of the two doors open first to relieve the pressure or vacuum on one side of the door prior to allowing the larger door to open. However, increases in initial expense and maintenance of extra moving parts are involved when a staged opening device is used at higher differentials.
The subject invention eliminates several problems related to the use of the above described flap valve or gate-lock valves.